N.H. Code Admin. R. Saf-C 5804.08
A vehicle will pass the opacity test if its smoke measurement is at or below the following levels for the model years indicated:
Table 2. Opacity Standards
Opacity Level
Model Year of Truck
40%
1991 and newer
55%
1974 to 1990
70%
1973 and older
Source. #6887, EXEMPT, eff 1-1-99